1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a transflective liquid crystal display device and a fabricating method thereof by using a reduced number of masks.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices are developed as next generation display devices because of their characteristics of light weight, thin profile, and low power consumption.
In general, an LCD device is a non-emissive display device that displays images utilizing optical anisotropy properties of liquid crystal materials that are interposed between a thin film transistor (TFT) array substrate and a color filter (C/F) substrate. Presently, among the various type of LCD devices commonly used, active matrix LCD (AM-LCD) devices in which thin film transistors (TFTs) are disposed in a matrix for each pixel region have been developed because of their high resolution and superiority in displaying moving images.
FIG. 1 is a schematic cross-sectional view of a liquid crystal display device according to the related art.
In FIG. 1, first and second substrates 2 and 4 are spaced apart and facing each other, and a liquid crystal layer 6 is interposed therebetween. A gate electrode 8 is formed on an inner surface of the second substrate 4 and a gate insulating layer 9 is formed on the gate electrode 8. A semiconductor layer 11 including an active layer 11a and an ohmic contact layer 11b is formed on the gate insulating layer 9 over the gate electrode 8. Source and drain electrodes 13 and 15 are formed on the semiconductor layer 11. The source and drain electrodes 13 and 15 are spaced apart from each other, and the active layer 11a corresponding to a space between the source and drain electrodes 13 and 15 functions as a channel “ch.” The gate electrode 8, the semiconductor layer 11, and the source and drain electrodes 13 and 15 constitute a thin film transistor (TFT) “T.” Even though not shown in FIG. 1, a gate line connected to the gate electrode 8 is formed along a first direction and a data line connected to the source electrode 13 is disposed along a second direction crossing the first direction. A pixel region “P” is defined by a cross of the gate line and the data line. A passivation layer 19 including a drain contact hole 17 is formed on the TFT “T” and a pixel electrode 21 connected to the drain electrode 15 through the drain contact hole 17 is formed in the pixel region “P.”
A color filter layer 23 corresponding to the pixel electrode 21 is formed on an inner surface of the first substrate 2. The color filter layer transmits only light of a specific wavelength. A black matrix 27 is formed at a border between the adjacent color filter layers 23 to prevent a light leakage and an inflow of ambient light into the TFT “T.” A common electrode 29 is formed on the color filter layer 23 and the black matrix 27 to apply a voltage to the liquid crystal layer 6. To prevent a leakage of the liquid crystal layer 6, a peripheral portion of the first and second substrates 2 and 4 is sealed with a seal pattern 31. A spacer 33 is disposed between the first and second substrates 2 and 4 to keep a uniform cell gap with the seal pattern 31. A first orientation film (not shown) can be formed between the common electrode 29 and the liquid crystal layer 6, and a second orientation film (not shown) can be formed between the liquid crystal layer 6 and the pixel electrode 21 to induce an alignment of the liquid crystal layer 6.
Even though not shown in FIG. 1, the LCD device includes a backlight unit under the second substrate 4 as a light source. However, the incident light from the backlight unit is attenuated during the transmission so that the actual transmittance is only about 7%. Accordingly, the backlight unit of the LCD device requires high brightness, thereby increasing power consumption by the backlight unit. Thus, a relatively heavy battery is required to supply a sufficient power to the backlight unit of such a device, and the battery cannot be used outdoors for a long period of time because of the increased power requirements.
In order to overcome the problems described above, a reflective LCD device and a transflective LCD device have been developed. The reflective LCD device uses the ambient light instead of light from the backlight unit, and thus it is light weight and easy to carry. In addition, power consumption of the reflective LCD device is reduced so that the reflective LCD device can be used for a portable display device such as an electronic diary or a personal digital assistant (PDA). In the reflective and transflective LCD devices, a reflective layer of a metallic material having a high reflectance is formed in a pixel region. The reflective layer can be formed in the pixel region over or under a transmissive electrode. More recently, the transmissive electrode is formed over the reflective layer to induce an alignment of the liquid crystal layer easily. Even with this structure, a transflective LCD having a multiple-layered insulating layer is suggested for protection of the reflective layer and to prevent an electrical short between the transmissive electrode and the reflective layer.
FIGS. 2A to 2G are schematic cross-sectional views showing a fabricating process of a display region of an array substrate for a transflective liquid crystal display device including a multiple-layered insulating layer according to the related art, and FIGS. 3A to 3G are schematic cross-sectional views showing a fabricating process of a non-display region of an array substrate for a transflective liquid crystal display device including a multiple-layered insulating layer according to the related art. Patterns on the array substrate are formed through a mask process including a deposition, a coating, a photolithography and an etching, and figures are shown according to a number of the mask process.
In FIGS. 2A and 3A, a gate electrode 10 and a first align key 12 of a first metallic material are formed on a substrate 4 through a first mask process.
In FIGS. 2B and 3B, after a gate insulating layer 14 of a first insulating material is formed on the gate electrode 10 and the first align key 12, a semiconductor layer 16 including an active layer 16a of amorphous silicon (a-Si) and an ohmic contact layer 16b of impurity-doped amorphous silicon (n+ a-Si) is formed on the gate insulating layer 14 over the gate electrode 10 through a second mask process.
In FIGS. 2C and 3C, source and drain electrodes 18 and 22 of a second metallic material are formed on the semiconductor layer 16 through a third mask process. The source and drain electrodes 18 and 22 are spaced apart from each other. At the same time, a data line 20 connected to the source electrode 18 is formed on the gate insulating layer 14, and a second align key 24 is formed on the gate insulating layer 14 over the first align key 12. The gate electrode 10, the semiconductor layer 16, and source and drain electrodes 18 and 22 constitute a thin film transistor (TFT) “T.”
In FIGS. 2D and 3D, after first, second and third passivation layers 25, 26 and 28 are sequentially formed on the TFT “T” and the second align key 24, a first open portion 30 exposing the second align key 24 is formed in the first, second and third passivation layers 25, 26 and 28 through a fourth mask process. The first open portion 30 is for preventing the second align key 24 from being screened by the relatively thick second passivation layer 26. Thus, a mask for the fourth mask process can have a simpler structure than that of the previous first to third mask processes.
In FIGS. 2E and 3E, a reflective layer 32 of a third metallic material having a high reflectance is formed on the third passivation layer 28 over the TFT “T” through a fifth mask process. The reflective layer 32 has a second open portion 34 exposing the third passivation layer 28. In this step of forming the reflective layer 32, the second align key 24 is used for the fifth mask process. The first and third passivation layers 25 and 28 are made of silicon nitride (SiNx), and the second passivation layer 26 is made of benzocyclobutene (BCB). The first passivation layer 25 is formed to improve an electrical property of the TFT “T.” The second passivation layer 26 is formed to reduce an electrical interference between the reflective layer 32 and a transmissive electrode (not shown). The third passivation layer 28 is formed to improve a contact property between the second passivation layer 26 and the reflective layer 32.
In FIGS. 2F and 3F, after a fourth passivation layer 36 is formed on the reflective layer 32 and the second align key 24, a drain contact hole 38 exposing the drain electrode 22 is formed in the first to fourth passivation layers 25, 26, 28 and 36 corresponding to the second open portion 34 through a sixth mask process. The fourth passivation layer 36 is made of the same material as the first and second passivation layers 25 and 28. The fourth passivation layer 36 is formed to prevent the Galvanic phenomenon (a corrosion phenomenon) between the reflective layer 32 and the transmissive electrode (not shown).
In FIGS. 2G and 3G, a transmissive electrode 40 of a transparent conductive material is formed on the fourth passivation layer 36 in a pixel region “P” through a seventh mask process. The transmissive electrode 40 is connected to the drain electrode 22 through the drain contact hole 38. The pixel region “P” includes a reflective portion corresponding to the reflective layer 32 and a transmissive portion. Images are displayed by using an ambient light in the reflective portion, while images are displayed by using light from the backlight unit (not shown) in the transmissive portion.
As shown in FIGS. 2A to 2G and FIGS. 3A to 3G, an array substrate for a transflective LCD device is formed through seven mask processes including a gate process, a semiconductor layer process, a data process, a reflective layer process, an align key open process, a contact hole process and a transmissive electrode process. Thus, the process of an array substrate for a transflective LCD device has more fabrication steps than that for a transmissive LCD device, and chemical and/or physical processes are repeated in the mask process. Therefore, as the fabrication steps increase, a fabrication cost and a possibility of damages to the device also increase.